Facebook Messenger has reached one billion monthly users, making it one of the most popular apps in the world.

Just two years after the app was separated from the main Facebook app, the Messenger app is catching up with its parent-app that has 1.5 billion active users a month.

"We're grateful for all the people who are sending billions of messages every day and we hope to send 1 billion thank yous in the form of a new floating balloon gift that everyone can use to celebrate," said a spokesman for Facebook.

To send the celebratory emoji, open the Messenger app and send a balloon emoji. The person receiving the message will see a stream of balloons fly up their screen when they read it.

Reaching the milestone earns Messenger a place in the top three most popular apps in the world, along with Facebook and WhatsApp, all three of which are owned by Mark Zuckerberg's company. It also makes it the second most popular iOS app of all time, according to the company.

"We remain focused on helping connect people to the people and businesses who matter most," said David Marcus, the vice president of Messenger.

Facebook wants users to interact with brands as well as their friends on Messenger through chat bots. The artificial intelligent conversationalists let users chat to brands for tasks such as ordering pizza, hunting for clothes and finding a job.

There are now more than 18,000 bots on Messenger and over 23,000 developers have signed up to develop chat bots, according to the company.

As well as the two Facebook apps and WhatsApp, the Silicon Valley giant also owns Instagram, the photo sharing app that reached 500 million users last month. The company grew the app by 25 per cent in 9 months, adding over 10 million new users per month - a rate of growth that far outpaces Facebook and Twitter.

Along with the news of Messenger's growth, the company also revealed that more than 22 million gifs are sent every day through the app, and that people have played 1.2 billion games of Facebook's secret basketball game.